"You just feel lucky you're one of the survivors," Thaler said. "As miserable as I was, as sick as I was, I wasn't on a ventilator."

CDC guidelines recommend anyone who tests positive to remain in isolation for at least seven days since symptoms first appeared and at least three days since recovery. Thaler said she tripled that and stayed isolated for 21 days and had been asymptomatic for a week.

"I met all of those criteria, so I went out into the world and luckily my first trip to the world was to give blood," she said.

She went to a New York City hospital to donate her blood. The antibodies in her plasma could be used to help critically ill COVID-19 patients.

The nurse took her blood and gave her a second test -- a patient needs to test negative before becoming a plasma donor.

To Thaler's surprise, she tested positive, and the test came three weeks after the onset of symptoms.

"My concern is there are a lot of people who are not going to get that second test, and they're going out into the world thinking that they're over the virus and they are immune," she said. "The truth is the virus lives in your body a lot longer than we think," she said.

She also said she received many mixed messages depending on who she talked to about her positive result.

"Some people said I had to isolate for two weeks, some people said I had to isolate for a week, and one person said no, it just means you had COVID-19," said Thaler. "When they give me information on the phone that's conflicting, they apologize and say 'this is new for us, we are not really sure' so that's frightening to me. It's better to err on the side of caution."She's urging everyone to stay home and to take the virus seriously. Thaler still plans on donating her plasma to patients in need, but it will now take at least another week in isolation to do so.

"To save one person is to save a world, and what better thing to do," she said.

The CDC has issued recommendations for patients who test positive to get two negative tests before heading out of isolation, but it's based on whether the tests are available and lab capacity.

Meanwhile, Thaler has continued to teach her kindergarten class for self-isolation through video conferencing.